The present invention relates to a seam construction for an OPW air bag woven fabric, particularly for passenger restraint systems.
With one-piece woven (OPW) air bags currently in use featuring single- and multi-ply portions to which a sealing coat, e.g. a film, is applied, there is the risk in the woven plane of gas escaping in single-ply portions simultaneously forming a seam-like link for the multi-ply portions brought together therein, because the coating intended to seal the air bag is applied only to the top and bottom, i.e. not preventing escape of the gas at the sides. Known from DE 103 26 757 A1 is a woven seam construction for an OPW air bag in which a coating can penetrate deeper into the woven fabric due to a woven construction in the single-ply portion of the seam having a looser weave. Although this construction is suitable to enhance the seam seal in the woven plane it still fails to produce satisfactory results as to its safety. In the single-ply portions at least three layers, namely the top coating as the first layer, the single-ply woven portion as the second layer and the bottom coating as the third layer are arranged one on top of the other. The woven material sandwiched between the coatings having a certain thickness, is by nature not a seal and can thus permit passage of the gas through the woven fabric in the woven plane between the coatings or films. This results in making it difficult to attain the useful duration demanded of air bags nowadays, particularly as regards side or head air bags, unless the gas loss is made up for by means of costly “inflators which supplement the escaped gas e.g. over several stages. “Useful duration” in this sense is the duration of an air bag remaining substantially inflated in cushioning the passenger after activation by vehicle impact. The gas loss also involves compensating a large quantity of gas generant, if need be. Yet a further drawback is that seam leakage may allow gas to gain access to the vehicle interior injurious to passengers by the gas itself and its high temperature.
An object of the invention is to propose a seam construction which avoids or at least diminishes the drawbacks of prior art. This object is achieved by a seam construction as it reads from claim 1, characterized by a woven seam having a single-ply seam portion surrounded by an at least a two-ply portion, the individual plies of which each comprise a looser woven structure than that of the single-ply portion. This improved seam construction in accordance with the invention makes it possible to achieve a substantially higher seal of an OPW air bag, since the quantity of gas escaping by leakage can now be substantially reduced, because coatings on the woven fabric can now penetrate very deeply into the woven fabric in the region of the seam in thus minimizing the spacing of the coatings from each other. This now makes it much easier to attain the wanted long useful duration.
In one advantageous aspect of the invention the seam construction is characterized in that the two-ply portion comprises the same number of threads as that of the single-ply portion, ensuring to advantage a harmonized weave with a minimum of distortions. In another advantageous aspect of the invention the seam construction is characterized in that the two-ply portion comprises an upper ply and a lower ply, both of which differ from the single-ply portion by each having a looser woven construction. This now makes it possible to customize the depth to which a coating penetrates on both sides of the woven fabric. This is particularly of advantage in transitions from a two to four or more ply air bag woven fabric when the side “facing the pressure side”, in other words, the side which receives the pressure of the inflation gas—as a rule the inner side of the air bag—needs to have a woven structure other than that of the opposite side.
In still another advantageous aspect of the invention the seam construction is characterized in that the upper ply has a plain weave L1/1 and the lower ply a basket weave P3/3, it having been discovered that such a construction is most expedient particularly in minimizing distortions in the weave. In yet a further advantageous aspect of the invention the seam construction is characterized in that the woven seam comprises a single-ply seam portion surrounded by a three-ply portion to further enhance the advantage of presetting the individual woven structure and the penetration capacity of the coatings. In another advantageous aspect the seam construction is characterized in that the three-ply portion comprises the same number of threads as the single-ply portion enhancing to advantage the ability to create a harmonized weave in minimizing distortions therein.
In yet a further advantageous aspect of the invention the seam construction is characterized in that the three-ply portion features an upper ply, a middle ply and a lower ply, each having a looser woven structure than that of the single-ply portion. This basically further increases to advantage the possibilities of varying the weave whilst simplifying setting individual woven portions to predefined woven construction requirements, in addition to making for an even better penetration of the coatings into the woven structure. In still another advantageous aspect of the invention the seam construction is characterized in that the upper ply and the lower ply are interconnected here and there. The purpose of this is to prevent or at least make it difficult that the plies become parted or separated from each other when chambers of pressure build up in the air bag between the plies because of the woven structure between the coatings of the sealed portions. What is generally to be appreciated as being novel is that the nature of sealing the seam in accordance with the invention is now achieved not just by a single-ply seam weave or by a looser fabric weave, but by a multi-ply woven construction or combination of single and multi-ply woven constructions.